Optoelectronic Devices Based On Lateral Grown Zinc Oxide Nanorods

Zinc oxide (ZnO), which is a direct wide band gap (3.37eV at room temperature) semiconductor with a large exciton binding energy of60meV, has attracted a wide range of interest in science and technology. Moreover, one-dimensional ZnO nanostructures are especially attractive because of their unique properties such as high surface-to-volume ratio and carrier confinement in two dimensions, which could improve device performance. Because of the unique optical, electronic, mechanical, and piezoelectric properties, ZnO nanostructures based field effect transistors, ultraviolet (UV) laser, UV photodetectors, strain sensor, field emission (FE) device, piezoelectric transducer, and solar cells have been studied extensively. Via controlled gowth of ZnO nanostructures, a series of high quality nano-photoelectric devices have been achieved in this dissertation.Through repeatable experiment, we found some materials can inhibit the growth of ZnO nanorods in hydrothermal approach. And using the combined effect from ZnO seed layer and these catalytically inactive layers, we have achieved selective edge growth and lateral growth of ZnO nanorods. Via tuning the experiment parameters, the detailed growth mechanism have been investigated. On the other hand, we have also used simple thermal evaporation method to get various ZnO nanostructures with high crystalline quality.Basically, ZnO nanostructures are potentially good FE materials. However, in reality, they are usually closely packed or bundled, resulting in severe screen effect which could depresses their FE performance. While in this dissertation, via selective edge growth of ZnO nanorods, the density of the ZnO nanorods can be controlled effectively, and the screen effect among the neighbourhood ZnO nanorods can be largely suppressed, and then, the field emission performance of the ZnO nanorod arrays has been improved. In addition, we have also fabricated density controlled ZnO nanorod arrays on carbon cloth with intrinsic three-dimensional pattern via simple thermal evaporation method. Moreover, through using this kind of density-controllable ZnO nanorod arrays with large surface-to-volume ratio as template to grow carbon nanotubes (CNTs) could further increase the emitter aspect ratio, decrease the screen effect, achieve large emission current density and thus enhance the FE performance. For these novel ZnO-CNT heterostructure FE arrays, a low turn-on field of0.4V/μm, a threshold field of0.84V/μm, a current density of4.48mA/cm at a field of1.34V/μm, and a field enhancement factor as high as4.9×104were ultimately obtained. And during a5h FE stability test, no obvious degradation of current density was observed and the emission current fluctuation was less than5%at1.04V/μm. Meanwhile, through the lateral growth of ZnO nanorods, we have firstly reported the lateral FE from ZnO nanorods. Through experiment and electrostatic field simulation, we found that the performance of the lateral FE device is strongly dependent on the vacuum separation distance.Generally, the fabrication process of lateral nano-photoelectric device is usually complicated and time-consuming. But in this dissertation, using the lateral growth mode of ZnO nanorods, we have fabricated various metal-semiconductor-metal structured lateral photoelectric devices, including UV photodetector, field effect transistor, strain sensor, strain driving transistor and electro-mechanical coupled logic circuits, by a single step hydrothermal reaction. We have tried to improve the performance of these devices by modifying the growth parameters and device structure. In addition, the detailed working mechanism of these devices has been researched and discussed. It has been found that the Schottky contact barrier has played a critical role in the electric transportation mechanism of these devices, and we can control the electric transportation performance of these devices in turn via tuning the Schottky contact barrier. Through these efforts, ZnO nanorod UV photodetector with responsivity of61A/W in365nm, ZnO nanorod field effect transistor with "On"-"Off" ratio of0.6×105, ZnO nanorod strain sensor with gauge factor of6.7×108, and various electro-mechanical coupled logic circuits such as NAND, NOR, XOR, MUX and DEMUX have finally been achieved.